Over the recent years, a fuel cell has been focused as a power source that is excellent in terms of operation efficiency and environmental compatibility. The fuel cell is capable of outputting the electric power in response to a request of a load by controlling a quantity of supply of fuel gas, however, there is a case in which the output voltage of the fuel cell is not coincident with the voltage requested by the load. Such being the case, a technology (refer to e.g., Patent documents 1 and 2) is proposed, which makes the output voltage of the fuel cell coincident with the voltage requested by the load in such a way that a DC-DC converter converts the output voltage of the fuel cell.
The DC-DC converter includes an electronic switch, a diode and an inductance as basic elements, and converts the voltage through a switching operation of the electronic switch. The DC-DC converter, a ripple being caused by the switching operation of the electronic switch, includes a snubber circuit for absorbing this ripple. The snubber circuit absorbs the ripple with a capacitor. If an electric charge accumulated in this capacitor is not effectively utilized, energy conversion efficiency of the DC-DC converter decreases, and hence there is proposed a technology of effectively utilizing the electric charge accumulated in the capacitor by regenerating the electric charge, and so on (refer to e.g., Patent documents 3-7)
[Patent document 1] Japanese Patent Laid-Open Publication No. 2007-228781
[Patent document 2] Japanese Patent Laid-Open Publication No. 2003-217625
[Patent document 3] Japanese Patent Laid-Open Publication No. H08-116663
[Patent document 4] Japanese Examined Patent Publication No. H07-75459
[Patent document 5] Japanese Patent Laid-Open Publication No. H06-189444
[Patent document 6] Japanese Patent Laid-Open Publication No. 2005-143259
[Patent document 7] Japanese Patent Laid-Open Publication No. H10-164709